1. Field Of The Invention
The invention relates to a new process for the production of 2-substituted-5-chlorimidazole-4-carbaldehydes of the general formula: ##STR2## wherein R means an alkyl group, a cycloalkyl group, a benzyl group, or a phenyl group. The alkyl group can be straight-chained or branched C.sub.1 -C.sub.6 -alkyl groups, such as, methyl, ethyl, propyl, isopropyl, n-butyl, sec. butyl, tert. butyl, pentyl and hexyl groups. A preferred alkyl group is the n-butyl group. Cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl groups are representatives of the cycloalkyl group. Both the benzyl and the phenyl group can contain substituents, such as, the aforementioned alkyl groups plus halogen atoms, nitro groups and amino groups.
2. Background Art
Several methods for the production of the mentioned compounds according to general formula I are known.
U.S. Pat. No. 4,355,040 describes a process according to which 2-amino-3,3-dichloro-acrylonitrile is reacted with an aldehyde to the corresponding azomethine intermediate product and further with an hydrogen halide and water to the 2-substituted-5-haloimidazole-4-carbaldehyde. Experimental data is lacking in such patent. But a great drawback of the synthesis is that the 2-amino-3,3-dichloroacrylonitrile used first has to be produced starting from dichloroacetonitrile by its reaction with hydrogen cyanide/sodium cyanide. The extremely toxic reactant and the safety measures associated with it that are already necessary for the preparation of the initial product, make the entire process unsuitable for industrial-scale production.
U.S. Pat. No. 4,355,040 discloses in another variant a three-stage process, in which, in a first stage, an amidinehydrochloride is ring closed with high NH.sub.3 pressure with dihydroxyacetone, the imidazole alcohol is halogenated and finally oxidized to aidehyde. It turned out that pressures of over 20 bars are necessary for the ring closure reaction. The oxidation of the alcohol works according to U.S. Pat. No. 4,355,040 in the presence of chromium oxide.
It is obvious that an oxidation with heavy metal oxides, that are not recyclable as a rule, are no longer justifiable from present ecological aspects.